Assessment of a proposed "three-criteria" cocaine addiction model for use in reinstatement studies with rats

RATIONALE

Relapse is a primary obstacle in the treatment of addiction disorders, and as such, understanding this phenomenon is a major effort of clinical and preclinical studies of cocaine addiction.

OBJECTIVE

A recently developed protocol uses laboratory rats to model cocaine addiction by examining three criteria of addiction-like behaviors (persistent seeking in the absence of drug, high motivation for drug, and resistance to punishment during drug seeking) to detect subjects that possess an addiction phenotype. We closely followed this protocol in order to detect rats possessing this addiction phenotype, with the goal of utilizing this model in future studies investigating potential therapies for relapse in human cocaine addicts.

RESULTS

The majority of the rats used in this study exhibited multiple characteristics thought to be associated with addiction-like behavior in rats, including robust reinstatement to multiple stimuli and high motivation to obtain cocaine. However, no rats displayed the complete addiction phenotype as previously described, due to a complete lack of addiction-like behavior in all subjects on two of the three addiction criteria (drug seeking in the absence of drug and resistance to punishment).

CONCLUSIONS

Our data highlight the independence of behavioral aspects of a rat addiction-like phenotype and suggest that some of these behavioral criteria may be altogether absent in some rat populations. Furthermore, our results suggest a closer review and analysis of some parameters used in this protocol and its global utility.

Systems level neuroplasticity in drug addiction

Drug addiction is a chronic relapsing disorder for which research has been dedicated to understand the various factors that contribute to development, loss of control, and persistence of compulsive addictive behaviors. In this review, we provide a broad overview of various theories of addiction, drugs of abuse, and the neurobiology involved across the addiction cycle. Specific focus is devoted to the role of the mesolimbic pathway in acute drug reinforcement and occasional drug use, the mesocortical pathway and associated areas (e.g., the dorsal striatum) in escalation/dependence, and the involvement of these pathways and associated circuits in mediating conditioned responses, drug craving, and loss of behavioral control thought to underlie withdrawal and relapse. With a better understanding of the neurobiological factors that underlie drug addiction, continued preclinical and clinical research will aid in the development of novel therapeutic interventions that can serve as effective long-term treatment strategies for drug-dependent individuals.

A rodent "self-report" measure of methamphetamine craving? Rat ultrasonic vocalizations during methamphetamine self-administration, extinction, and reinstatement

Rats emit ultrasonic vocalizations (USVs) in a variety of contexts, and it is increasingly clear that USVs reflect more complex information than mere positive and negative affect states. We sought to examine USVs in a common model of addiction and relapse, the self-administration/reinstatement paradigm, in order to gain insight into subjective states experienced by rats during various types of methamphetamine seeking. We measured three subtypes of "50kHz" USVs [flats, trills, and non-trill frequency modulated (FM) USVs], as well as long and short duration "22kHz" USVs, during self-administration and extinction training, and during reinstatement elicited by cues, a methamphetamine prime, cues+prime, or the pharmacological stressor yohimbine. During self-administration and extinction, rats emitted many flats and FMs, (and short duration "22kHz" USVs on day 1 of self-administration), but few trills. In contrast, methamphetamine priming injections potently enhanced FMs and trills, and trill production was correlated with the degree of methamphetamine+cue-elicited reinstatement. Cues alone yielded increases only in flat USVs during reinstatement, though a subset of rats displaying strong cue-induced reinstatement also emitted long duration, aversion-related "22kHz" USVs. Although yohimbine administration caused reinstatement, it did not induce "22kHz" USVs in methamphetamine-experienced or methamphetamine-naïve rats (unlike footshock stress, which did induce long duration "22kHz" USVs). These findings demonstrate heterogeneity of rat USVs emitted during different types of methamphetamine seeking, and highlight their potential usefulness for gaining insight into the subjective states of rats in rodent models of drug addiction and relapse.

Nicotine self-administration and reinstatement of nicotine-seeking in male and female rats

BACKGROUND

Tobacco addiction is a relapsing disorder that constitutes a substantial worldwide health problem, with evidence suggesting that nicotine and nicotine-associated stimuli play divergent roles in maintaining smoking behavior in men and women. While animal models of tobacco addiction that utilize nicotine self-administration have become more widely established, systematic examination of the multiple factors that instigate relapse to nicotine-seeking have been limited. Here, we examined nicotine self-administration and subsequent nicotine-seeking in male and female Sprague-Dawley rats using an animal model of self-administration and relapse.

METHODS

Rats lever pressed for nicotine (0.03 and 0.05 mg/kg/infusion, IV) during 15 daily 2-h sessions, followed by extinction of lever responding. Once responding was extinguished, we examined the ability of previously nicotine-paired cues (tone+light), the anxiogenic drug yohimbine (2.5mg/kg, IP), a priming injection of nicotine (0.3mg/kg, SC), or combinations of drug+cues to reinstate nicotine-seeking.

RESULTS

Both males and females readily acquired nicotine self-administration and displayed comparable levels of responding and intake at both nicotine doses. Following extinction, exposure to the previously nicotine-paired cues or yohimbine, but not the nicotine-prime alone, reinstated nicotine-seeking in males and females. Moreover, when combined with nicotine-paired cues, both yohimbine and nicotine enhanced reinstatement. No significant sex differences or estrous cycle dependent changes were noted across reinstatement tests.

CONCLUSIONS

These results demonstrate the ability to reinstate nicotine-seeking with multiple modalities and that exposure to nicotine-associated cues during periods of a stressful state or nicotine can increase nicotine-seeking.

Corticotrophin releasing factor (CRF) induced reinstatement of cocaine seeking in male and female rats

Significant sex differences have been demonstrated in clinical and preclinical studies of cocaine addiction, with some of the most consistent differences noted in regard to the role of stress and craving. The current study examined stress-induced reinstatement of cocaine seeking in male and female rats in an animal model of relapse using corticotropin-releasing factor (CRF) administration. Both male and female rats demonstrated increased cocaine seeking in response to CRF. CRF-induced reinstatement was highly variable across both male and female rats, and further analysis revealed a subpopulation that was particularly sensitive to CRF (high responders). Female high responders displayed significantly increased responding to CRF compared to males. Individual differences in stress responsivity could thus contribute to the likelihood of relapse, with females showing greater heterogeneity to stress-induced relapse.

Enhancement of cue-induced reinstatement of cocaine-seeking in rats by yohimbine: sex differences and the role of the estrous cycle

RATIONALE

Previous studies have shown that female rats exhibit enhanced cocaine-seeking across several phases of the addiction cycle when compared to males. Drug-seeking in females is also estrous cycle dependent and inversely associated with plasma progesterone. Although sex and estrous cycle-dependent differences have been reported in the reinstatement of cocaine-seeking triggered by cocaine injections or drug-paired cues, it is not yet known what role the estrous cycle may have on stress-induced reinstatement, either alone or in combination with drug-paired cues.

OBJECTIVES

Here, we examined male and female rats for reinstatement of extinguished cocaine-seeking produced by cocaine-paired cues or the stress-activating drug, yohimbine.

METHODS

Male and female Sprague-Dawley rats self-administered intravenous cocaine (0.5 mg/kg/infusion) paired with a light + tone stimulus for 10-14 days. Lever responding was then allowed to extinguish, with subsequent reinstatement testing occurring 30 min following an injection of yohimbine (1.25 or 2.5 mg/kg, intraperitoneal) or vehicle either in the presence or absence of the conditioned stimulus.

RESULTS

While males and females showed similar cue- and yohimbine-induced reinstatement (3-4 times over "No Cue"-vehicle responding), combining these stimuli resulted in a robust enhancement in cocaine-seeking in both groups, with a greater increase in females (10-12 vs. 14-15 times over "No Cue"-vehicle responding for the males and females, respectively). When examined as a function of the estrous cycle, females in proestrus demonstrated higher levels of responding during yohimbine + cues reinstatement.

CONCLUSIONS

This cycle-dependent enhanced sensitivity to stress enhancement of cocaine-paired cues may generalize to greater relapse susceptibility under stressful conditions.

Repeated aripiprazole administration attenuates cocaine seeking in a rat model of relapse

RATIONALE

Aripiprazole (Abilify) is an atypical antipsychotic drug characterized by partial agonist activity at dopamine (DA) D(2)/D(3) receptors and a low side-effect profile. While we previously demonstrated that acute aripiprazole blocked the reinstatement of cocaine seeking in an animal model of relapse, clinical treatment of relapse prevention necessitates testing the effects of aripiprazole following prolonged abstinence, as well as after repeated administration during withdrawal from cocaine.

OBJECTIVES

We assessed the effects of repeated aripiprazole treatment on cocaine seeking after abstinence and during conditioned cue-induced and cocaine-primed reinstatement in rats.

MATERIALS AND METHODS

Rats self-administered intravenous cocaine paired with a light + tone stimulus for 10-14 days, followed by 2 weeks of abstinence. Following post-abstinence relapse testing, lever responding was allowed to extinguish, with subsequent reinstatement testing occurring either in the presence of the conditioned stimulus, or after a cocaine-priming injection (10 mg/kg, intraperitoneal (IP)). Following 3 or 7 days of pretreatment, rats received an injection of aripiprazole (0.25, 0.5, and 1.0 mg/kg, IP) or vehicle prior to post-abstinence relapse and reinstatement testing.

RESULTS

Vehicle-pretreated animals showed robust cocaine seeking during relapse and reinstatement testing, an effect that was significantly attenuated by aripiprazole pretreatment, although no lasting effects were found in the absence of acute injection.

DISCUSSION

These findings support the possibility that repeated aripiprazole may be an effective therapeutic agent for the prevention of relapse in abstinent cocaine users. Based on its antipsychotic profile, aripiprazole may be particularly useful for individuals diagnosed with comorbid psychoses, such as schizophrenia or bipolar disorder.

The neurocircuitry of addiction: an overview

Drug addiction presents as a chronic relapsing disorder characterized by persistent drug-seeking and drug-taking behaviours. Given the significant detrimental effects of this disease both socially and economically, a considerable amount of research has been dedicated to understanding a number of issues in addiction, including behavioural and neuropharmacological factors that contribute to the development, loss of control and persistence of compulsive addictive behaviours. In this review, we will give a broad overview of various theories of addiction, animal models of addiction and relapse, drugs of abuse, and the neurobiology of drug dependence and relapse. Although drugs of abuse possess diverse neuropharmacological profiles, activation of the mesocorticolimbic system, particularly the ventral tegmental area, nucleus accumbens, amygdala and prefrontal cortex via dopaminergic and glutamatergic pathways, constitutes a common pathway by which various drugs of abuse mediate their acute reinforcing effects. However, long-term neuroadaptations in this circuitry likely underlie the transition to drug dependence and cycles of relapse. As further elucidated in more comprehensive reviews of various subtopics on addiction in later sections of this special issue, it is anticipated that continued basic neuroscience research will aid in the development of effective therapeutic interventions for the long-term treatment of drug-dependent individuals.

NMDA receptor blockade in the basolateral amygdala disrupts consolidation of stimulus-reward memory and extinction learning during reinstatement of cocaine-seeking in an animal model of relapse

Previous research from our laboratory has implicated the basolateral amygdala (BLA) complex in the acquisition and consolidation of cue-cocaine associations, as well as extinction learning, which may regulate the long-lasting control of conditioned stimuli (CS) over drug-seeking behavior. Given the well established role of NMDA glutamate receptor activation in other forms of amygdalar-based learning, we predicted that BLA-mediated drug-cue associative learning would be NMDA receptor dependent. To test this hypothesis, male Sprague-Dawley rats self-administered i.v. cocaine (0.6 mg/kg/infusion) in the absence of explicit CS pairings (2-h sessions, 5 days), followed by a single 1-h classical conditioning (CC) session, during which they received passive infusions of cocaine discretely paired with a light+tone stimulus complex. Following additional cocaine self-administration sessions in the absence of the CS (2-h sessions, 5 days) and extinction training sessions (no cocaine or CS presentation, 2-h sessions, 7 days), the ability of the CS to reinstate cocaine-seeking on three test days was assessed. Rats received bilateral intra-BLA infusions (0.5 microl/hemisphere) of vehicle or the selective NMDA receptor antagonist, 2-amino-5-phosphonovalerate (AP-5), immediately prior to the CC session (acquisition), immediately following the CC session (consolidation), or immediately following reinstatement testing (consolidation of conditioned-cued extinction learning). AP-5 administered before or after CC attenuated subsequent CS-induced reinstatement, whereas AP-5 administered immediately following the first two reinstatement tests impaired the extinction of cocaine-seeking behavior. These results suggest that NMDA receptor-mediated mechanisms within the BLA play a crucial role in the consolidation of drug-CS associations into long-term memories that, in turn, drive cocaine-seeking during relapse.

The role of dorsal vs ventral striatal pathways in cocaine-seeking behavior after prolonged abstinence in rats

RATIONALE

Recent studies have implicated an important role for the dorsal striatum during craving for cocaine and in cocaine-seeking after abstinence in rats.

OBJECTIVES

We compared the effects of pharmacological inactivation of mesencephalic dopamine (DA) cell body regions and dorsal vs ventral striatal terminal fields in an animal model of relapse after chronic cocaine self-administration.

MATERIALS AND METHODS

Rats self-administered cocaine for 2 h/day for ten sessions, followed by 2 weeks of abstinence (i.e., no extinction training). Immediately before being returned to the self-administration chamber, we assessed the effects of gamma-aminobutyric acid agonist inhibition of midbrain DA regions (substantia nigra [SN] and ventral tegmental area [VTA]) and striatum (dorsolateral caudate-putamen, nucleus accumbens core, and nucleus accumbens shell) on relapse to cocaine-seeking in the absence of reinforcement. Further testing examined daily extinction responding subsequent to the initial relapse test.

RESULTS

Inactivation of the dorsal caudate-putamen and midbrain regions attenuated cocaine seeking, while inactivation of the ventral striatum had no such effects. However, subsequent sessions under extinction conditions revealed a rebound in cocaine seeking in animals that had undergone inactivation in all regions except the dorsolateral caudate-putamen.

CONCLUSIONS

The dorsal but not ventral striatum plays a critical role in cocaine seeking immediately after abstinence. These data support the theory that chronic cocaine may shift activity from the ventral to dorsal striatum during drug seeking under certain conditions. While not necessary at the time of relapse, the ventral striatum appears to be involved in processing critical information of the relapse event.

Plasma progesterone levels and cocaine-seeking in freely cycling female rats across the estrous cycle

Previous studies have reported sex and estrous cycle-dependent differences in the reinstatement of cocaine-seeking triggered by cocaine injections or drug-paired cues. However, the relationship between estradiol or progesterone levels and cocaine-seeking in a reinstatement model of relapse has not been explored. Thus, we examined changes in plasma hormone levels during cocaine-taking and -seeking behaviors in gonadally intact female rats. Rats self-administered cocaine (0.5mg/kg infusion) during daily 2-h sessions, followed by extinction. For reinstatement, cocaine (0, 5, or 10mg/kg, i.p.) was administered 30 min prior to testing. Vaginal smears and blood samples were collected prior to and during chronic cocaine self-administration, extinction, and reinstatement testing. Relative to non-estrous females, females in estrus showed greater responding during self-administration, extinction, and during cocaine-primed reinstatement. The highest progesterone levels were noted at the time of lowest cocaine-seeking (proestrus) and the lowest levels of progesterone occurred at the time of highest cocaine-seeking (estrus). In contrast, plasma estradiol levels did not show any clear pattern with cocaine-seeking. These data from an animal model of relapse supports recent clinical evidence that progesterone reduces subjective craving in cocaine-dependent women. Overall, these results suggest that progesterone administration may be a useful intervention for reducing the incidence of relapse.

Modeling the anxiety-depression continuum hypothesis in domestic fowl chicks

Anxiety and depression are currently classified as separate clinical syndromes despite considerable similarities in their symptoms, pathophysiological substrates and response to treatment interventions. An alternative hypothesis views anxiety and depression along a temporal continuum, a construct that the current research attempts to model in a preclinical setting. In experiment 1, socially raised domestic fowl chicks separated from conspecifics demonstrated a pattern of distress vocalizations that sequentially models anxiety-like and depressive-like states. In addition, administration of the benzodiazepine anxiolytic chlordiazepoxide and the tricyclic antidepressant imipramine provided pharmacological validation for the model in that they were capable of dissociating the anxiety-like and depressive-like states. In experiment 2, corticosterone levels were quantified across the isolation test session to provide convergent validity to the model. These findings fit well with the human clinical literature on the anxiety-depression continuum perspective, and suggest the consideration of a nosology that emphasizes the inter-relatedness of these clinical states rather than their boundaries.

Aripiprazole blocks reinstatement of cocaine seeking in an animal model of relapse

BACKGROUND

Aripiprazole (Abilify) is an atypical antipsychotic drug primarily characterized by partial agonist activity at dopamine (DA) D2 receptors and low side effects. Based on pharmacologic properties that include a stabilization of mesocorticolimbic DA activity, a pathway implicated in addiction, aripiprazole was tested for its ability to prevent relapse to cocaine seeking in rats.

METHODS

We assessed the dose-dependent effects of aripiprazole on conditioned cue-induced and cocaine-primed reinstatement of drug-seeking behavior following chronic intravenous cocaine self-administration in an animal model of relapse.

RESULTS

Aripiprazole potently and dose-dependently attenuated responding on the previously cocaine-paired lever during both reinstatement conditions, with slightly greater efficacy at reducing conditioned-cued reinstatement. Aripiprazole was effective at doses that failed to alter cocaine self-administration, food self-administration, reinstatement of food-seeking behavior, or basal locomotor activity, suggesting selective effects of aripiprazole on motivated drug-seeking behavior.

CONCLUSIONS

These results in a relapse model show that aripiprazole can block cocaine seeking without affecting other behaviors. The D2 partial agonist properties of aripiprazole likely account for the blockade of reinstatement of cocaine-seeking behavior. Given its established efficacy and tolerability as a treatment for psychosis, aripiprazole may be an excellent therapeutic choice for reducing craving and preventing relapse in people with cocaine dependency.

Potentiation of cue-induced reinstatement of cocaine-seeking in rats by the anxiogenic drug yohimbine

Stress and drug-associated cues can trigger drug desire and relapse in abstinent cocaine users. Although the role of these two factors in relapse is well documented, it remains unclear as to whether an interaction between stress and drug-associated cues can lead to an enhancement in cocaine-seeking behavior. Here, we assessed the effects of the anxiogenic alpha2-noradrenergic receptor antagonist, yohimbine, on reinstatement of cocaine-seeking in rats either in the presence or absence of cocaine-associated cues. Yohimbine pretreatment in the absence of cocaine-associated cues or cues by themselves reliably reinstated responding on the previously cocaine-paired lever (3-4 times higher than extinction levels). However, animals showed greatly potentiated responding if yohimbine preceded cue-induced reinstatement (10-13 times higher than extinction levels, or 3-5 times over cues or yohimbine alone). While cocaine self-administration produced a significant increase in plasma corticosterone, plasma corticosterone levels did not show a clear relationship to cocaine-paired lever responding during cue and/or yohimbine-induced reinstatement. These results demonstrate that exposure to drug-paired cues during a stressful state can greatly potentiate cocaine-seeking and suggest that future treatment interventions should target multiple modalities.

The role of the basolateral amygdala in stimulus-reward memory and extinction memory consolidation and in subsequent conditioned cued reinstatement of cocaine seeking

The consolidation of cue-cocaine associations and extinction learning (i.e. cue-no cocaine associations) into long-term memory probably regulates the long-lasting control of conditioned stimuli (CS) over cocaine-seeking behaviour, and the basolateral amygdala (BLA) may play a role in this phenomenon. To test this hypothesis, rats previously trained to self-administer cocaine underwent a single classical conditioning (CC) session, during which they received passive pairings of cocaine infusions and a novel light + tone stimulus complex. After additional self-administration sessions in the absence of CS presentation and subsequent extinction training sessions, the ability of the CS to reinstate cocaine-seeking on five test days was assessed. Rats received intra-BLA microinfusions of vehicle or the Na+-channel blocker tetrodotoxin (TTX) immediately after CC (consolidation of CS-cocaine associations) or immediately after reinstatement testing (consolidation of extinction learning). TTX administered immediately after CC attenuated subsequent CS-induced reinstatement. In contrast, TTX administered after the first reinstatement test impaired the extinction of cocaine-seeking behaviour during a second reinstatement test by disrupting extinction memory. Overall, these findings suggest that Na+ channel-mediated mechanisms within the BLA mediate the consolidation of both cocaine-stimulus association and extinction learning, two processes that have opposite effects on subsequent cue-induced cocaine-seeking behaviour.

Screening antidepressants in the chick separation-stress paradigm

RATIONALE

Clinical research has indicated that antidepressants are efficacious in the treatment of anxiety disorders, especially when repeatedly administered. However, few animal models of anxiety are sensitive to antidepressants, a finding that may be due to procedures limited to acute administrations.

OBJECTIVES

The purpose of the present research was to further validate the chick separation-stress paradigm as an animal model of anxiety by examining its sensitivity to the monoamine oxidase inhibitor (MAOI) phenelzine (6.25, 12.5, 25.0 mg/kg), the tricyclic antidepressant (TCA) imipramine (5.0, 10.0, 20.0 mg/kg), the selective serotonin reuptake inhibitor (SSRI) citalopram (1.0, 2.5, 5.0 mg/kg), and the norepinephrine reuptake inhibitor (NRI) maprotiline (5.0, 10.0, 20.0 mg/kg) under acute (no pretreatment) or repeated (3 or 6 days pretreatment) administration procedures.

METHODS

Following any pretreatment, 8-day-old chicks received their respective vehicle or drug probe injection 15 min before tests in either a "mirror" (low stress) or "no mirror" (high stress) condition for a 180-s isolation period. The dependent measures were distress vocalizations to index separation stress and sleep onset latency to index sedation.

RESULTS

The model was sensitive to acutely administered phenelzine (MAOI), imipramine (TCA), and maprotiline (NRI), but not citalopram (SSRI) and retained its sensitivity to these drug probes across both repeated administration procedures. None of the drug probes possessed any sedative properties.

CONCLUSIONS

These results help extend the validity and utility of the chick separation-stress paradigm as an animal model of anxiety by demonstrating its sensitivity to antidepressants under both acute and repeated administration procedures.

High-performance liquid chromatographic determination of xanthohumol in rat plasma, urine, and fecal samples

Xanthohumol (XN) is the major prenylated flavonoid in hop plants and as such a constituent of beer. Pharmacological studies have shown that XN possesses marked antioxidant and antiproliferative effects. In order to study the resorption and metabolism of this compound, reversed-phase high-performance liquid chromatography is used for the determination of XN in rat plasma, urine, and feces. In session one, rats receive either oral or intravenous (iv) administration (20 mg/kg body weight) of XN. In session two, rats receive oral administration of 50, 100, 200, 400, and 500 mg/kg body weight XN for bioavailability studies at various dose levels. Plasma, urine, and feces are collected at varying time points and assayed for their XN content. Plasma levels of XN fell rapidly within 60 min after iv administration; no XN is detected in plasma after oral administration in either session. XN and its metabolites are excreted mainly in feces within 24 h of administration. The method is a reliable tool for performing studies of XN in different biological material.

Anti-inflammatory and anti-hyperalgesic effects of sesquiterpene lactones from Magnolia and Bear's foot

Sesquiterpene lactones possess a variety of biological activities, including anti-inflammatory activity. Two plants native to the southeastern United States, Magnolia grandiflora (L.) and Smallanthus uvedalius (L.) [syn Polymnia uvedalius (L.)], are novel sources of the sesquiterpene lactones parthenolide and enhydrin, respectively. In this study, the anti-inflammatory and anti-hyperalgesic effects of these isolated lactones from these two plant sources were evaluated in the rat carrageenan inflammation model. Rats received ip injections of either vehicle (propylene glycol), indomethacin (5 mg/kg), 11,13-dihydroparthenolide (20 mg/kg), parthenolide (5 or 20 mg/kg) or enhydrin (5 or 20 mg/kg). A 100-microl injection of 2.0% carrageenan was made into the plantar surface of the right hindpaw. Paw withdrawal latencies and paw volumes in both inflamed and non-inflamed paws were recorded at four test intervals: pre-inflammation baseline (0 time point), and 1, 2 and 4 h post-carrageenan injection. Vehicle-treated animals exhibited a significant time-dependent hyperalgesic and edema response that was greatest at the 4-h test interval. Indomethacin significantly blocked the hyperalgesic response and modestly attenuated the edema response. Parthenolide (20 mg/kg) and enhydrin (20 mg/kg) significantly blocked the hyperalgesic response and significantly attenuated the edema response; 11,13-dihydroparthenolide did not affect either inflammation or hyperalgesia. These findings suggest that parthenolide and enhydrin from these plant sources may be useful in the treatment of inflammatory pain.

Corticosterone response in the chick separation-stress paradigm

Corticosterone response to separation stress and its sensitivity to the anxiolytic, chlordiazepoxide (CDP), were examined in 7-day-old domestic fowl (Gallus gallus). Saline or CDP (8.0 mg/kg) was injected intramuscularly 30 min before tests. Chicks were placed in isolation either with or without mirrors for a 15-min observation period, in which distress vocalizations were recorded. After testing, chicks were euthanized and blood was collected for the corticosterone assay. Chicks tested in the No-Mirror condition displayed an increase in vocalizations that was attenuated by CDP. Similarly, corticosterone levels were highest in chicks tested in the No-Mirror condition; however, CDP only modestly attenuated corticosterone levels. The present findings demonstrate that corticosterone levels parallel the behavioral marker of distress vocalizations in this paradigm, but this biological marker may be less sensitive than the behavioral marker to benzodiazepine anxiolytic manipulations.

Dissociation of stress behaviors in the chick social-separation-stress procedure

Separation from conspecifics in chicks produces an increase in distress vocalizations and a decrease in response to a noxious stimulus (stress-induced analgesia). This study questioned the relative contributions of novelty to the test chamber and social separation in mediating these stress responses. Eight-day-old chicks were tested either in isolation or in the presence of two social companions for a 3-min observation period in which distress vocalizations were recorded as well as the frequency of footlifts in response to a 50-microl injection of 0.10% formalin into the plantar surface of the footpad. In Expt. 1, chicks received six, 3-min test chamber habituation trials (vs. no habituation) one per day before testing; in Expt. 2, chicks were tested with mirrors placed in the chambers (vs. no mirrors). In both studies, isolated chicks in control groups (i.e., no habituation or no mirror) exhibited increased distress vocalizations and decreased nociceptive responses. In Expt. 1, habituation to the test chamber attenuated stress-induced analgesia but did not affect distress vocalizations. In Expt. 2, placement of mirrors in the test chamber attenuated distress vocalizations but did not affect stress-induced analgesia. These findings demonstrate a dissociation of stress behaviors in the chick social-separation-stress procedure: the stress-induced analgesia response is primarily mediated by novelty to the test apparatus while the distress vocalizations response is mediated by separation from conspecifics.

Anxiolytic effects of kava extract and kavalactones in the chick social separation-stress paradigm

RATIONALE

Piper methysticum extract (kava kava) possesses numerous therapeutic properties, but it is unknown which of its principle constituents (kavalactones) subserve such effects.

OBJECTIVES

This experiment sought to characterize the putative anxiolytic properties of P. methysticum extract and its six principle kavalactones in the chick social separation-stress paradigm.

METHODS

Eight-day-old chicks received intraperitoneal injections of either vehicle, chlordiazepoxide (5.0 mg/ml per kg), P. methysticum extract (containing 30% kavalactones), kavain, dihydrokavain, methysticin, dihydromethysticin, yangonin, or desmethoxyyangonin (30 mg/ml per kg for kava compounds) 30 min prior to being tested in the presence of two conspecifics or in isolation for a 3-min observation period. Latency to adopt a ventral recumbent posture to index sedation, number of vocalizations to index separation distress, and a composite pain score (in response to 50 microliters 0.10% formalin injection into the plantar surface of the foot) to index stress-induced analgesia served as dependent measures.

RESULTS

Both chlordiazepoxide and P. methysticum extract attenuated separation-induced distress vocalizations and stress-induced analgesia. Dihydrokavain attenuated separation-induced distress vocalizations.

CONCLUSIONS

These findings suggest that the anxiolytic effects of P. methysticum extract may be mediated, in part, by dihydrokavain.

Anxiolytic properties of botanical extracts in the chick social separation-stress procedure

RATIONALE

The recent growth in sales of natural products labeled as dietary supplements in the United States has renewed scientific interest in the study of the therapeutic effects of multi-component botanical products.

OBJECTIVES

This study sought to determine whether botanical extracts derived from the Rutaceae family, Acori graminei, the Magnoliaceae family, Alchemilla vulgaris and Primula veris, which had previously been identified in bioassays as having potential anxiolytic activity, were active in the chick social separation-stress procedure.

METHODS

Eight-day-old chicks received IP injections of test articles 30 min before being tested in the presence of two social companions or in isolation for a 3-min observation period. Dependent measures were: a) latency to adopt a ventral recumbent posture to index sedation, b) number of vocalizations to index separation-distress and c) a composite pain score (comprised of footlift frequency and footlift duration in response to 50 microl of 0.10% formalin injected into the plantar surface of the foot) to index stress-induced analgesia.

RESULTS

Proprietal extracts NPS00033 from the Rutaceae plant family and NPS00039 (Relora) from the Magnoliaceae plant family screened positive in this chick model without causing sedation.

CONCLUSIONS

These results suggest that botanical extracts Relora and NPS00033 may be useful in modulating anxiety states.